Tuberculin conversion rate after BCG vaccination of apparently healthy infants in a resource-poor setting

Abstract

Background: Although Bacillus Calmette Guerin (BCG) vaccine remains one of the most important public health preventive measures against tuberculosis (TB), the presence of a BCG scar may not imply an immune response. Tuberculin reactivity after BCG vaccination has been the most common measure of the effect of the BCG vaccine. Post-vaccination BCG-induced tuberculin reactivity ranges from no induration to an induration diameter of 15 mm. However, tuberculin conversion in infants is usually about 10 mm in more than 90% of infants tested at 12 weeks post-vaccination age. Objective: This study sought to assess the tuberculin conversion rate after BCG vaccination. Materials and Methods: It was a hospital-based cross-sectional study. Two hundred and eighty (280) infants aged 13 to 15 weeks who received BCG vaccination within one month of birth were enrolled. The BCG scar diameter was measured, and Mantoux test was done. Data were analyzed by using the Statistical Package for Social Sciences (SPSS), version 20 (Chicago Il). Results: Among the 280 BCG-vaccinated infants, tuberculin conversion rate was 64%, whereas scar failure rate was 28.9%. Overall, 75.9% of infants with a BCG scar had a positive Mantoux test. The BCG-vaccinated infants with a BCG scar were about six times more likely to have a tuberculin conversion than those without a BCG scar (OR =5.641, 95% C.I = 3.227 to 9.859). Conclusion: There was a 64% conversion rate among the BCG-vaccinated infants. The presence of the BCG scar correlated well with the tuberculin conversion rate.

Keywords

• bcg
• mantoux
• scar failure
• tuberculin conversion